Open questions related to machine learning and Tensorflow

This contains a number of things related to machine learning, Python, Tensorflow and related frameworks which I've been wondering about and haven't found a solution so far. (That is, had not found a solution when I last maintained this page. :-) ) If you have ideas, I'd be happy if you contact me!

• Is there any sensible documentation about input and output parameters if you write custom loss functions? The Model.fit documentation seems rather vague to me.